The invention relates to a tensioning machine for the heat treatment of lengths of material which are guided widthways, particularly lengths of textile material.
In tensioning machines, particularly the more modern tensioning machines, the tensioning chains intended to convey the lengths of material through the machine frequently travel around at relatively high speeds and are also subjected to relatively high treatment temperatures. The links of these tensioning chains are provided at their joints with so-called high-temperature grease, but the operational life thereof depends not only upon the chain stress but also to a considerable extent upon the temperature stress which derives from the prevailing chain temperature.
Attempts have therefore been made to keep the chain temperature as low as possible in order thereby to increase the operational life of the high-temperature grease which is used. Thus for example it has already been proposed for this purpose inter alia (cf. German Patent document DE-OS 35 26 584) to associate cooling air blowing arrangements with the chain guide rails of a tensioning machine in the long sections located in the region of the material inlet zone and/or the material outlet zone. In this way, cold air should be blown onto the sections of the tensioning chain running above all in the region outside the heat treatment zones so that these sections of the chain are cooled to some extent thereby. However, when this known construction of a tensioning machine is put into practice the tensioning chain only cools by a relatively small amount (for example by relatively few .degree.C.), which does not lead to any effective lengthening of the operational life of the high-temperature grease usually used in tensioning chains, and a disadvantage of this is that the expected operational life is a function of the operating temperature of the grease.
As a further disadvantage of the known tensioning machine, it should also be mentioned that in it the strands of the tensioning chain running forwards and backwards have cooling air blown onto them from below, i.e. through bores provided in the bearing surfaces. The structural work necessary for this in the region of the chain guide rails involve considerable additional expense.